Leakage characterization for electronic circuit temperature monitoring

ABSTRACT

An electronic system can be used to monitor temperature. The electronic system can include a characterized dielectric located adjacent to a plurality of heat-producing electronic devices. The electronic system can also include a leakage measurement circuit that is electrically connected to the characterized dielectric. The leakage measurement circuit can be configured to measure current leakage through the characterized dielectric. The leakage measurement circuit can also be configured to convert a leakage current measurement into a corresponding output voltage. A response device, electrically connected to the leakage measurement circuit can be configured to, in response to the output voltage exceeding a voltage threshold corresponding to a known temperature, initiate a response action.

BACKGROUND

The present disclosure generally relates to an electronic system. Inparticular, this disclosure relates to an electronic system configuredto self-monitor an operating temperature and react to an operatingtemperature above a temperature threshold.

A printed circuit board (PCB), can be used to mechanically support andelectrically connect electronic components using conductive paths orsignal traces etched from copper sheets laminated onto non-conductivedielectric substrates. Multiple copper/insulator layer pairs, also knownas “cores,” can be laminated together in the fabrication of the PCB. Thenumber and arrangement of cores can be designed to fit the needs of avariety of applications.

Vertical interconnect structures (vias) can be used to interconnectconductive signal traces between various conductive layers within thePCB. Copper shapes or areas can be used for power and grounddistribution to components mounted on the PCB. The interconnectstructures in the PCB can be designed to be physically and electricallycompatible with the components the PCB can be used to interconnect.

Flexible printed circuits, also referred as “flex circuits,” or “flexcables,” can be generally understood to be similar to a PCB that canbend. In practice, however, the set of design rules, e.g., conductorwidths and spacings, used to design and fabricate flex circuits can varysignificantly from design rules used in the design and fabrication ofrigid or semi-rigid PCBs. In some applications, the conductors of a flexcircuit can be fabricated using process such as photo imaging or laserimaging as the pattern definition method rather than “printing”processes.

A flexible printed circuit includes a metallic layer of traces, oftencopper, bonded to a dielectric layer such as polyimide. The thickness ofthe metal layer can range from very thin, e.g., less than 0.0001″ tovery thick, e.g., greater than 0.010″, and the dielectric thickness cansimilarly vary in a range between 0.0005″ and 0.010″. An adhesivematerial or other types of bonding such as vapor deposition, can be usedto bond the metal to the substrate. Because copper tends to readilyoxidize in the presence of air, exposed copper surfaces are oftencovered with a protective layer. Gold or solder are common materialsused for this purpose, due to their electrical conductivity andenvironmental durability. For non-contact or non-conductive areas adielectric material can be used to protect the circuitry from oxidationor electrical shorting. Electrical leakage, i.e., current leakage, canoccur through dielectric materials located between adjacent metalliclayers.

SUMMARY

Embodiments can be directed towards an electronic system for temperaturemonitoring. The electronic system includes a characterized dielectriclocated adjacent to a plurality of heat-producing electronic devices anda leakage measurement circuit, electrically connected to thecharacterized dielectric. The leakage measurement circuit is configuredto measure current leakage through the characterized dielectric andconvert a leakage current measurement into a corresponding outputvoltage. The electronic system also includes a response device,electrically connected to the leakage measurement circuit. The responsedevice is configured to, in response to the output voltage exceeding avoltage threshold corresponding to a known temperature, initiate anaction.

Embodiments can also be directed towards a method for designing anelectronic system for temperature monitoring. The method includesreceiving design requirements for the electronic system andcharacterizing dielectric and adhesive materials that are candidates foruse in the electronic system. The method further includes choosing, fromcandidate dielectric and adhesive materials, dielectric and adhesivematerials in accordance with the design requirements. The method furtherincludes designing a characterized dielectric to include chosendielectric and adhesive materials and fabricating the characterizeddielectric in accordance with a characterized dielectric design. Themethod further includes integrating the characterized dielectric intothe electronic system by populating the electronic system with aplurality of heat-producing electronic devices and electricallyinterconnecting the characterized dielectric to a leakage measurementcircuit.

Embodiments can also be directed towards a method for operating anelectronic system for temperature monitoring. The method includesreceiving, with a characterized dielectric, heat from adjacentheat-producing electronic devices and measuring, with a leakagemeasurement circuit, current leakage through the characterizeddielectric. The method further includes converting, with the leakagemeasurement circuit, measured current leakage into a correspondingoutput voltage and comparing, with a response device electricallyinterconnected to the leakage measurement circuit, the correspondingoutput voltage to a high-voltage threshold. The comparing is done todetect a characterized dielectric temperature greater than ahigh-temperature threshold. The method further includes initiating, inresponse to the temperature of the characterized dielectric exceedingthe high-temperature threshold, an action with the response device.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated into,and form part of the specification. They illustrate embodiments of thepresent disclosure and, along with the description, serve to explain theprinciples of the disclosure. The drawings are only illustrative ofcertain embodiments and do not limit the disclosure.

FIG. 1 depicts an electronic system for temperature monitoring,according to embodiments of the present disclosure.

FIG. 2 is a flow diagram depicting a method for designing an electronicsystem for temperature monitoring, according to embodiments consistentwith the figures.

FIG. 3 includes a graph depicting dielectric leakage measurements fortwo dielectric materials, according to embodiments consistent with thefigures.

FIG. 4 is a flow diagram depicting a method for operating an electronicsystem for temperature monitoring, according to embodiments consistentwith the figures.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

In the drawings and the Detailed Description, like numbers generallyrefer to like components, parts, steps, and processes.

DETAILED DESCRIPTION

Certain embodiments of the present disclosure can be appreciated in thecontext of providing temperature monitoring, through a leakagemeasurement circuit, for electronic equipment such as servers, which maybe used to provide data to clients attached to a server through anetwork. Such servers may include, but are not limited to web servers,application servers, mail servers, and virtual servers. While notnecessarily limited thereto, embodiments discussed in this context canfacilitate an understanding of various aspects of the disclosure.Certain embodiments may also be directed towards other equipment andassociated applications, such as providing temperature monitoring,through a leakage measurement circuit, for computing systems, which maybe used in a wide variety of computational and data processingapplications. Such computing systems may include, but are not limitedto, supercomputers, high-performance computing (HPC) systems, and othertypes of special-purpose computers. Embodiments may also be directedtowards providing temperature monitoring, through a leakage measurementcircuit, for consumer and small office/home office (SOHO) electronicequipment such as personal computers, laptops, mobile and network serverdevices.

For ease of discussion, the term “FR” is used herein, in reference to aclass of Fire Retardant glass fiber epoxy laminate materials. FRmaterials, particularly FR4, are commonly used in the construction of awide variety of PCBs. FR4 is designed for use in high-densitymulti-layer printed circuit boards (PCBs) and is suitable for highvolume fine-line/multi-layer applications.

Similarly, the term “AP” is generally used herein, in reference to aclass of Adhesiveless/high-Performance laminate materials that include acopper-clad laminate and an all-polyimide composite of polyimide filmbonded to copper foil. Such materials can be used in constructingmultilayer flex and rigid flex applications which require advancedmaterial performance, temperature resistance and high-reliability.

The term “HT” is generally used herein, in reference to a class of HighTemperature laminate materials that feature favorable material andelectrical characteristics. Such materials can have a higher glasstransition temperature (T_(g)) and lower loss characteristics (e.g.,loss tangent) than materials such as FR4.

Increasing power dissipation and internal temperatures of electronicsystems such as computers, supercomputers, servers, network and telecomequipment and the like have been continuing, long-term industry trends.Internal operating temperatures that exceed specified limits can poseserious risks to electronic system components such as PCBs, integratedcircuits (ICs) and power supply units. A PCB, for example, operating ata temperature approaching T_(g) can experience a change of materialstate, delaminate, outgas, and/or lose mechanical/structural integrity.

In order to mitigate the risk of thermal-related electronic systemfailures, which can be catastrophic to both electronic hardware as wellas to data integrity, improved system cooling and temperature monitoringfeatures can be implemented. Such temperature monitoring systems can usediscrete temperature sensing devices that monitor temperature at asingle point within the electronic system. In response to a sensed“over-temperature” condition, a variety of corrective actions can beinitiated in order to restore the operating temperature of the systemwithin a specified and safe range.

Such “single-point” or even “multiple-point” temperature monitoringsystems, however, can easily produce inaccurate electronic systemtemperature measurements. A discrete temperature sensor can produce aninaccurate reading resulting from the temperature at the sensor locationnot correlating to the overall or average temperature of the electronicsystem. For example, a discrete sensor can be located in a relativelycool location of the system, e.g., near a cooling air intake vent, or itcan be located adjacent to an electronic device having a relatively highthermal output such as a processor. In either scenario, the discretesensor may provide inaccurate temperature measurements, which can causeany corresponding response action to be initiated too frequently, or notfrequently enough. Either of these scenarios can be detrimental toperformance and reliability of the electronic system.

Embodiments of the present disclosure are directed towards a temperaturemonitoring system for an electronic system such as a computer,supercomputer, server, and the like. The temperature monitoring systemincludes a characterized dielectric that serves as atemperature-dependent resistor, and that is integrated into a PCB orflexible circuit. The integration of the characterized dielectric into aPCB or flexible circuit allows it to receive heat from a number ofheat-producing electronic devices within the electronic system, and notsimply from a single or small number of heat-producing electronicdevices. The physical size of the host PCB or flexible circuit ensuresthat the characterized dielectric does not act a discrete or “point”temperature sensor, thus eliminating that problems associated with suchsensors, as described above. A leakage measurement circuit is used toconvert a characterized dielectric leakage current into a voltageproportional to a temperature of the characterized dielectric. Anelectrically interconnected response device is used to initiatecorrective actions in response to one or more temperature thresholdsbeing crossed.

Various aspects of the present disclosure can be useful for sensing andmonitoring electronic system temperature changes without usingindividual/discrete external temperature sensors. An electronic systemconfigured according to embodiments may sense, with one sensor, anoverall electronic system operating temperature more accurately than asystem configured with one or more discrete temperature sensors.

Embodiments can be configured to respond to violations of one or moreoperating temperature threshold(s) by initiating actions designed tomitigate a variety of temperature-related conditions. Such conditionscan include “over-temperature” conditions corresponding to temperaturesapproaching a T_(g) temperature at which PCB resins change state, beginto outgas, discolor, delaminate and/or lose structural integrity. A PCBapproaching T_(g) can also experience a change in electrical properties.By way of example, a T_(g) for FR4 dielectric materials can beapproximately 130° C. - 140° C. “Over-temperature” conditions can alsoinclude approaching a PCB ignition temperature.

Embodiments of the present disclosure can be useful in managingelectronic system design cost and complexity while using existing andproven PCB design methodologies and material sets. Embodiments of thepresent disclosure can be used to detect temperatures, either above orbelow preset temperature thresholds resulting from certain data securityand cryptography-related tampering events. Such events can includelow-temperature or high-temperature events. Embodiments can provide anon-mechanical, e.g., not bi-metallic, temperature sensor having nomechanical movement or deviation for use within electronic systems. Sucha sensor can have enhanced reliability relative to other types oftemperature sensing devices. Some embodiments of the present disclosurecan be useful in extremely cold, i.e., cryogenic or space environments.Aspects of the various embodiments can be used to monitor PCB productquality by detecting temperature values experienced by a PCB or flexiblecircuit during raw card manufacturing process.

An electronic system designed according to certain embodiments can becompatible with existing and proven computer, server, supercomputer andpersonal computer (PC) designs and PCB/flexible circuit designmethodologies and material sets. A electronic temperature monitoringsystem constructed according to embodiments of the present disclosurecan be installed within an existing electronic equipment enclosure.

Certain embodiments relate to an electronic system configured toself-monitor an operating temperature and react when the operatingtemperature is above or below a preset temperature threshold. FIG. 1includes consistent views 100 and 150 of an electronic system 102 fortemperature monitoring, according to embodiments of the presentdisclosure. View 100 can provide a visual understanding of electronicsystem 102 that includes a characterized dielectric 104 and anelectrically interconnected leakage measurement circuit 106 configuredto monitor the temperature of characterized dielectric 104. In responseto a sensed temperature of characterized dielectric 104 that is above orbelow a specified threshold, a response device 120 can initiate anaction designed to mitigate a thermal issue/condition within theelectronic system 102. It can be understood that electronic system 102can be integrated into a wide variety of electronic devices and systemssuch as computers, special-purpose computers and servers, as detailedabove. Such systems can rely on the monitoring of internal operatingtemperatures in order to ensure operation within a specified safeoperating temperature range.

While a particular component arrangement and interconnection scheme isdepicted in views 100, 150, a number of variations of these schemes arepossible that include the components depicted and described herein.Embodiments can be useful in providing accurate sensing of, and a timelyresponse to high-temperature operating conditions for an electronicsystem. Such sensing and timely response can be particularly useful inpreventing thermally-induced damage to hardware such as PCBs andelectronic components, and preserving the integrity of data stored onthe electronic system.

According to embodiments, characterized dielectric 104 has electricalproperties that cause it to function as a temperature-dependent resistorR_(L). For example, in embodiments, an increased temperature ofcharacterized dielectric 104 can cause current leakage through it toincrease, i.e., decrease the resistance of R_(L). Conversely, a decreasein characterized dielectric 104 temperature can cause current leakagethrough it to decrease, i.e., increase the resistance of R_(L). Thistemperature-dependent property of characterized dielectric 104 can makeit particularly useful as a reliable and predictable temperature-sensingdevice. The resistance R_(L) can be sensed and used as an indicator ofthe temperature of characterized dielectric 104.

In embodiments, characterized dielectric 104 includes dielectricmaterial(s) located between, and in electrically conductive contact withtwo conductive layers, which serve as electrical terminals. According toembodiments, the two electrically conductive layers can each be a planarstructure, such as a power plane of a PCB or flexible circuit. Accordingto embodiments, characterized dielectric 104 can be a portion of a PCB,e.g., 158, view 150 that is located adjacent to multiple heat-producingelectronic devices, e.g., 154, 156, 160, view 150, within electronicsystem 102. Similarly, in some embodiments, characterized dielectric 104can represent a portion of a flexible circuit (not depicted), locatedadjacent to multiple heat-producing electronic devices.

The above-described placement of characterized dielectric 104 can allowit to receive heat from multiple heat-producing electronic devices, andthus provide a relatively accurate and “broad” indication of thetemperature of the electronic system. Such an indication can be moreaccurate than a temperature indication from a discrete temperaturesensor that can be located, for example, adjacent to a single componentwith a particularly high thermal output, e.g., a processor, which couldprovide an inaccurate, e.g., artificially high temperature indication.

Resistance R_(L) of characterized dielectric 104 is part of voltagedivider circuit 116, which also includes resistor R1 (electricallyconnected to V_(DD)), sense net 112 and GND net 108. When interconnectedin such a circuit, the temperature-dependent value of R_(L) can bedetermined by measuring, with leakage measurement circuit 106, avoltage, on sense net 112, produced by current leakage I_(L) flowingthrough resistor R_(L). This sensing can be used to provide repeatablevoltages corresponding to specific operating temperatures of electronicsystem 102. The voltage at sense net 112 is subsequently amplified byleakage measurement circuit 106, in order to produce output voltageV_(s) at temperature output 110.

According to embodiments, leakage measurement circuit 106 can include anamplifier 114, which, in some embodiments, can be implemented as anoperational amplifier (op-amp). In such an implementation, the gain ofamplifier 114 can be determined by the ratio of the values of resistorR2 and resistor R3. Leakage measurement circuit 106 is depicted as anexample circuit; other types of leakage measurement circuits 106 arepossible. In embodiments, the functionality of leakage measurementcircuit 106 can be relatively simple to implement as discrete componentsor into an existing or new IC such as an application-specific integratedcircuit (ASIC). Embodiments can include other types and arrangements ofelectronic components used to implement leakage measurement circuit 106.In some embodiments, threshold detection circuitry/functionality can bedesigned into leakage measurement circuit 106.

In some embodiments, temperature output 110 can be a single analogsignal wire. In some embodiments, leakage measurement circuit 106 caninclude additional components, not depicted, configured to convertoutput voltage V_(s) into other type of signal(s), for example, adigital and/or high-speed serial signal representing output voltageV_(s). In corresponding embodiments, temperature output 110 can, forexample, including conductors configured to transmit a representation ofV_(s) as a high-speed serial signal such as a Universal Serial Bus (USB)signal.

Response device 120 is electrically connected to the leakage measurementcircuit 106 through temperature output 110 to receive output voltageV_(s). According to embodiments, response device 120 can include, but isnot limited to, a processor circuit, a service processor, and anetwork-connected device. In some embodiments, response device 120 isconfigured to, in response to the output voltage exceeding a voltagethreshold corresponding to a known high-temperature threshold ofcharacterized dielectric 104, initiate an action. According toembodiments, the action can include, but is not limited to, reducing aclock frequency of a heat-producing electronic component within theelectronic system 102, reducing power supplied to the electronic system102, increasing cooling of the electronic system 102 and disconnecting apower source from the electronic system 102. In embodiments, actions canalso include sending a message, e.g., text message, system consolemessage or Short Messaging Service (SMS) message alerting a system useror technician of a temperature above or below a specified threshold.Actions can also include sounding an audible alarm or illuminating avisual indicator such as a light-emitting diode (LED). One or acombination of the above-described actions can be useful for protectingboth the hardware of an electronic system and the integrity and securityof data contained therein.

The employment of characterized dielectric 104 as a temperature sensorwithin PCB 158 can be particularly useful with respect to protecting PCB158 from damage due to excessively high temperatures. The temperature ofPCB 158 that is directly sensed and responded to can be significantlymore accurate than temperature indications from discrete sensors whichmay not be directly correlated to a PCB 158 temperature. This directsensing can be useful for providing an enhanced level of protection forPCB 158. In some embodiments, a violation of either a high-voltage orlow-voltage threshold, corresponding to a high or low temperature,respectively, characterized dielectric 104 temperature can result fromtampering activity related to a data security device. According toembodiments, a variety of actions, e.g., alert messages or alarms, andmodification of hardware operation can be initiated based on acorresponding variety of high and low temperature thresholds beingcrossed.

According to embodiments, electronic system cross-sectional side view150 can be useful in providing a visual understanding of a portion ofelectronic system 102. The electrical characteristics, structure andfunction of characterized dielectric 104 are consistent with thosedescribed above in reference to electronic system 102. View 150 can beparticularly useful in depicting structural and thermal relationshipsbetween heat-producing electronic devices, e.g., ASIC 154 and component156, characterized dielectric 104 and PCB 158.

According to embodiments, PCB 158 can be an integral part of a computer,supercomputer, server, PC, or other electronic system. PCB 158 includescharacterized dielectric 104 and can also include heat-producingelectronic devices such as ASIC 154 and component 156, mounted on atleast one PCB or flexible circuit surface, and embedded device 160mounted within a cavity 162. These devices can include a variety ofcomponent types including, but not limited to processors, memory ICs,graphics processing units (GPUs), Peripheral Component InterconnectExpress (PCIe) switches and the like, consistent with ICs used incomputers, servers, and other electronic systems. Power plane pairs,i.e., a core such as characterized dielectric 104 that includesdielectric layer 166 and associated adhesive materials, can be selectedand included within a PCB 158 cross-section. In embodiments, adielectric layer, e.g., 166, can be chosen by a designer, based onmaterial characterization data, in order to conform to electronic systemdesign requirements.

Characterized dielectric 104 can be located in close proximity toheat-producing electronic devices such as 154, 156, to ensure thattemperatures measured through the use of characterized dielectric 104closely correspond to heat dissipated by multiple heat-producingelectronic devices. Characterized dielectric 104 can be particularlyuseful as a “broad” temperature sensing device that can provide accurateelectronic system temperature measurements without beingdisproportionately influenced by one particular heat-producingelectronic device. Characterized dielectric 104 is also useful insimultaneously providing power and ground distribution to electronicdevices within electronic system 102. The use of characterizeddielectric 104 can be helpful in managing and containing development andmanufacturing costs, design and fabrication complexity and area needsfor PCBs within an electronic system.

Example dielectric material types that can be used in characterizeddielectric 104 can include, but are not limited to Fire Retardant (FR),High Temperature (HT) and Adhesiveless/high-Performance (AP) laminatematerials layers. Conductive layers 164A and 164B, for example, can bepartial or full conductive planes or wiring traces used to deliver powerto various components mounted on surfaces of PCB 158. In accordance withPCB designs and material sets, conductive layers 164A and 164B caninclude copper and/or other types of metal.

According to embodiments, characterized dielectric 104 includes adielectric layer 166 of a PCB 158, with a face 170 of the dielectriclayer 166 adjacent to a conductive layer 164A of the PCB 158 and with anopposing face 172 of the dielectric layer 166 adjacent to a conductivelayer 164B of the PCB 158. In some embodiments, characterized dielectric104 can be employed as a single plane-pair, as depicted, or incorporatedinto a differential sensor that includes two or more plane pairs. Inembodiments, bonding film 168 can be used to bond characterizeddielectric 104 to another portion, for example other core layers, of PCB158.

Reference 158 is depicted in view 150 as a PCB, however, in someembodiments, 158 can alternately represent a flexible circuit which, forexample, can be used a point-to-point interconnection cable. In someembodiments, such a flexible circuit can include components mounted ontoone or more surfaces. According to embodiments, such a flexible circuitcan be located adjacent to a number of heat-producing electronic devicessuch as ASIC 154 and component 156.

FIG. 1 and the components depicted in FIG. 1 are not necessarilyrepresentative of the actual size of the components or subcomponentsindividually or collectively used in embodiments. They are notnecessarily a representation of the actual or relative size of anydevice, component of subcomponent. Rather, they are meant to depict howeach sub-component of an electronic system can be arranged relative toother sub-components in accordance with embodiments of the presentdisclosure.

FIG. 2 is a flow diagram depicting a method 200 for designing anelectronic system 102, FIG. 1 , for temperature monitoring, according toembodiments consistent with the figures. The execution of method 200 canbe useful in designing an electronic system that can provide reliable,cost-effective temperature monitoring and corrective action responsesfor use with electronic systems such as computers and servers. Inassociation with a functioning electronic system, method 200 can providerobust temperature monitoring and protection responses to the electronicsystem.

The method 200 moves from start 202 to operation 204. Operation 204generally refers to receiving design requirements for the electronicsystem 102, FIG. 1 , for temperature monitoring. According toembodiments, design requirements can include, for example, specifiedleakage characteristics of the characterized dielectric 104, FIG. 1 ,over a range of electronic system operating temperatures and a specifiedimpedance range, across the conductive layers, e.g., 164A, 164B, ofcharacterized dielectric 104, FIG. 1 . Other design requirements caninclude, for example, specified maximum voltage droop and energy lossacross the conductive layers of dielectric 104. According toembodiments, each of these requirements may need to be satisfied inorder to meet the overall design requirements for an electronic system.

According to embodiments, the design requirements can be received by acircuit designer or electronic design automation (EDA) system from aspecification document or file. Such a document or file can have, forexample, the form of a printed copy or electronic file. The electronicfile can have a variety of formats such as a word processing document,text file, spreadsheet file or a proprietary or non-proprietaryspecifications file.

It can be understood that various electronic systems can have a varietyof different design requirements. For example, one type of electronicsystem may be portable and/or depend at least partially on battery powerand may require a relatively small maximum dielectric leakage. Incontrast, another type of electronic system may not depend on batterypower, may have certain characteristics that are more compatible with aparticular leakage measurement circuit 106 design, and have acharacterized dielectric 104 with a larger specified maximum dielectricleakage. Once the design requirements have been received, the method 200moves to operation 206.

Optional operation 206 generally refers to characterizing candidatedielectric and adhesive materials for use within the electronic system100, 150, FIG. 1 . According to embodiments, candidate dielectric andadhesive materials can be characterized in order to provide PCB andcircuit designers with parameters that are useful in making designdecisions and tradeoffs. For example, a dielectric material can besubjected to various frequencies applied to conductive plates on planarsurfaces of the material, and resulting loss can be recorded. FIG. 3 isan example graph including plots of measured loss V_(s). frequency fortwo dielectric materials FR and HT. According to embodiments,characterizing candidate dielectric and adhesive can includecharacterizing electrical leakage properties, includingtemperature-dependant electrical leakage variation, of the candidatedielectric and adhesive materials. In embodiments, candidate dielectricand adhesive materials can include, but are not limited to, FR, HT andAP materials.

The above-described characterization can be performed by a vendor orsupplier of dielectric materials, by a circuit or PCB designer, or by anindependent lab, for example. Such characterization can be performed atone or more temperatures of interest, such as an anticipated maximumoperating temperature, or across an operating temperature range of anelectronic system. Once candidate dielectric and adhesive materials havebeen characterized, the method 200 moves to operation 208.

Operation 208 generally refers to choosing characterized dielectric andadhesive materials in accordance with the design requirements receivedin operation 204. According to embodiments, dielectric and adhesivematerials are chosen, by a designer, from a number of characterizeddielectric and adhesive materials, for example, FR, HT, and APdielectric materials. In some embodiments, a dielectric material and asupplemental dielectric material can be combined in order to takeadvantages of the electrical and/or physical properties of bothmaterials. One or more dielectric material can be chosen, based onvariety of properties individual materials and properties ofproportionally combined materials. These properties can include, forexample, temperature-dependent leakage and loss characteristics,dielectric constant and adhesion properties. Choices of dielectricmaterials can be made in conjunction with analysis of output from EDAprogram such as a field-solver or other electrical simulation program.Once the characterized dielectric and adhesive materials have beenchosen, the method 200 moves to operation 210.

Operation 210 generally refers to designing a characterized dielectricto include characterized dielectric and adhesive materials chosen inoperation 208. According to embodiments, designing a characterizeddielectric can include selecting a particular plane pair in a PCB orflexible circuit design and selecting a volume of characterizeddielectric material that satisfies dielectric leakage designrequirements. In some embodiments, more than one plane pair can be used,and in some embodiments, an EDA program such as a field-solver or othertype of electrical simulation program can be used in the design process.Once the characterized dielectric has been designed, the method 200moves to operation 212.

Operation 212 generally refers to fabricating a characterized dielectricin accordance with the characterized dielectric design completed inoperation 210. According to embodiments, the characterized dielectric104, FIG. 1 , can be fabricated in accordance with the design ofoperation 210, and subsequently bonded, for example, with bonding film168, FIG. 1 , to other layers of the PCB 158, FIG. 1 . Variouslamination, etching, drilling, and other process steps used in operation212 are generally consistent with existing PCB and/or flexible circuitfabrication and assembly processes. Once the characterized dielectrichas been fabricated, the method 200 moves to operation 214.

Operation 214 generally refers to integrating the characterizeddielectric, e.g., 104, FIG. 1 , into the electronic system 102, FIG. 1 .According to embodiments, the integrating can include populating theelectronic system 102 with a plurality of heat-producing electronicdevices, electrically interconnecting the characterized dielectric 104,FIG. 1 , to the leakage measurement circuit 106, FIG. 1 . In someembodiments, integrating can also include locating a flexible circuit104 adjacent to the plurality of heat-producing electronic devices. Oncethe characterized dielectric has been integrated into the electronicsystem, the method 200 may end at operation 216.

FIG. 3 is a graph depicting dielectric leakage measurements as afunction of frequency of two dielectric materials, according toembodiments consistent with the figures. Such dielectric materials canbe used in layers, e.g., dielectric layer 166, FIG. 1 , as may beincluded in a characterized dielectric 104. Characterization can includea wide variety of such dielectric materials including, but not limitedto FR, HT and AP dielectric layers.

Characterization & measurement of characteristics such as dielectricleakage can give a PCB designer valuable insight regarding whichdielectric materials or dielectric material combination(s) to choose fora particular application. The temperature-dependent electrical leakageof such dielectric materials can be useful in the measurement oftemperatures within an electronic system, e.g., 102, FIG. 1 .

The data plots provided in FIG. 3 can provide a visual understanding ofcausal relationships between measurement frequency and dielectricleakage, as well as the relative difference(s) in leakage betweenvarious types of dielectric materials. The vertical axis of FIG. 3corresponds to the leakage, measured in dB, of FR and HT type dielectricmaterials; a higher value or location on the vertical axis correspondsto a higher leakage value. The horizontal axis at the bottom of FIG. 3corresponds to a frequency (kHz) at which the leakage measurement istaken. By way of example, a range for the vertical axis can span fromapproximately -92 dB, at the bottom, to -70 db, at the top. Similarly, arange for the horizontal axis can span from approximately 0 kHz to 1.0kHz. Leakage measurements can be taken at a variety of temperatures,such as 25° C., 85° C. or 100° C.

It can be observed that the FR dielectric curve 302 and the HTdielectric curve 304 have appreciably different leakages. For example,at the maximum measurement frequency, (right side of FIG. 4 ) theleakage difference shown between FR dielectric curve 302 and the HTdielectric curve 304 is approximately 13 dB, corresponding to a 20Xdifference in power loss between the FR and HT dielectric materials.Measurements for other dielectric material types can yield otherrelative results. Characterization of dielectric materialcharacteristics such as leakage, as presented in FIG. 3 , can beparticularly useful for providing an understanding of the electricalcharacteristics of various dielectric material types, which can be usedin choosing between dielectric material types to include in acharacterized dielectric 104 design.

FIG. 4 is a flow diagram depicting a method 400 for operating anelectronic system 102, FIG. 1 , for temperature monitoring, according toembodiments consistent with the figures. The execution of method 400 canbe useful in providing self-monitoring of an electronic system operatingtemperature and in reacting to the operating temperature being above orbelow a temperature threshold. Method 400 can be executed without theneed for discrete temperature sensors, IC temperature sensors or remotemonitoring devices. When used in conjunction with a functioningelectronic system, method 400 can provide robust, accurate operatingtemperature monitoring and protection response actions to the electronicsystem.

The method 400 moves from start 402 to operation 404. Operation 404generally refers to receiving heat with characterized dielectric 104from heat-producing electronic devices within electronic system 102.According to embodiments, heat dissipated by heat-producing electronicdevices such as ASIC 154, component 156 and embedded device 160, FIG. 1, is received by a characterized dielectric 104 in close proximity,i.e., adjacent or in thermally conductive contact with theheat-producing electronic devices. According to embodiments, thetemperature-dependent resistance of characterized dielectric 104 canchange in response to a temperature change.

In some embodiments, the heat-producing electronic devices can be partsof an electronic system 102 that is a cryptography security systemincluding a cryptography module. Cryptographic modules can include butare not limited to a cryptographic coprocessor, a cryptographicaccelerator, a cryptographic adapter card, a cryptographic fieldprogrammable gate array (FPGA) and memory storing cryptographicaccelerator data.

Operation 404 can also include heating the characterized dielectric 104to a known or “reference” temperature. Such heating can be useful indetecting minor temperature variations, or in “normalizing” thetemperature of characterized dielectric 104 for compatibility withleakage measurement circuit 106. Once heat is received from electronicdevices by the characterized dielectric, the method 400 moves tooperation 406.

Operation 406 generally refers to measuring leakage current flowingthrough the characterized dielectric 104, FIG. 1 and converting, withleakage measurement circuit 106, FIG. 1 , the leakage currentmeasurement to an output voltage at temperature output 110. According toembodiments, leakage current leakage I_(L) flows through thetemperature-dependent resistance R_(L) of characterized dielectric 104,FIG. 1 , producing a temperature-dependent voltage on sense net 112,FIG. 1 . This voltage is received by amplifier 114 of leakagemeasurement circuit 106, FIG. 1 . According to embodiments, amplifier114 can be an operational amplifier (op-amp) configured to amplify avoltage received on sense net 112 at a positive “+” input.

Amplifier 114, FIG. 1 is configured, with electrically interconnectedresistors R2 and R3, to convert the leakage current measurement into anoutput voltage V_(s) on the temperature output 110. According toembodiments, the gain of amplifier 114 can be determined by the ratio ofvalues of resistor R2 and resistor R3. Once the leakage current has beenmeasured and converted to an output voltage, the method 400 moves tooperation 408.

Operation 408 generally refers to comparing, with response device 120,the output voltage at temperature output 110 to one or more voltagethreshold(s). According to embodiments, the output voltage V_(s) on thetemperature output 110 represents and corresponds to the temperature ofcharacterized dielectric 104, FIG. 1 .

Response device 120 is electrically interconnected to receive the outputvoltage V_(s) on the temperature output 110. According to embodiments,response device 120 can be, for example, a processor circuit, a serviceprocessor, a network-connected device, or other electronic device.Response device 120 includes circuits/functionality to receive outputvoltage V_(s), compare V_(s) to predetermined voltage thresholds(s) and,in response to V_(s) violating a threshold, initiate one or moreresponsive action(s).

In some embodiments, output voltage V_(s) is compared to a high-voltagethreshold, i.e., a “maximum” threshold corresponding to a maximumtemperature measured with characterized dielectric 104. By way ofexample, a “maximum” voltage threshold could be 1.1 V, which couldcorrespond to a maximum operating temperature of 130° C. for PCB 158,FIG. 1 . A temperature of 130° C. can correspond to a laminate Tg for anPCB constructed using FR4 laminate materials. Operating a PCB 158 above130° C. can result in irreversible damage, such as delamination, changeof state, outgassing, and the like. Other temperature thresholds cancorrespond to laminate ignition temperature(s) and dielectricdiscoloration temperature(s), for example.

Other types of dielectric materials can have other corresponding maximumoperating temperatures, which can be stored within response device 120and used as a basis for comparison. In some embodiments, output voltageV_(s) can be compared to a low-voltage threshold, i.e., a “minimum”threshold corresponding to a minimum temperature measured withcharacterized dielectric 104. Such a low-voltage threshold cancorrespond to a minimum operating temperature for PCB 158, FIG. 1 .

It can be understood that both high-voltage thresholds and low-voltagethresholds can be used to detect unauthorized tampering activities withelectronic equipment, for example equipment incorporating securityperimeters and/or other hardware security devices. In some embodiments,these thresholds can be in accordance with temperature thresholdsspecified by a published cryptosecurity specification. For example, sucha cryptosecurity specification can be the U.S. Government FederalInformation Processing Standard (FIPS) 140-2 Security Requirements forCryptographic Modules. Once the output voltage has been compared to thevoltage threshold(s), the method 400 moves to operation 410.

At operation 410, a determination is made by the response device 120,FIG. 1 , regarding whether the output voltage driven onto temperatureoutput 110, violates at least one voltage threshold. According toembodiments, response device 120 can compare the value of output voltageV_(s) received at temperature output 110 to one or more internallystored thresholds. One or more of each high-voltage and low-voltagethresholds can be stored within response device 120 and used as a basisfor comparison to output voltage output voltage V_(s). It can beunderstood that each voltage threshold corresponds to a particulartemperature of characterized dielectric 104. A “violation” of a voltagethreshold can be understood to include a value of output voltage V_(s)that is greater than a high-voltage threshold or a value of outputvoltage V_(s) that is less than a low-voltage threshold. By way ofexample, a value of output voltage V_(s) that is greater than ahigh-voltage threshold can corresponding to a temperature of PCB 158that presents a risk of irreversible damage. If the output voltagedriven onto temperature output 110 does not violate at least one voltagethreshold, the method 400 returns to operation 404. If the outputvoltage driven onto temperature output 110 violates at least one voltagethreshold, the method 400 moves to operation 412.

Operation 412 generally refers to initiating, with the response device120, FIG. 1 , in response to at least one voltage threshold beingviolated, an action. According to embodiments, response device 120 canperform an action, or can communicate with another device, e.g., acomputer, processor, IC, or network-connected or other electricallyinterconnected device to initiate the action. Actions can be initiatedin response to the violation of one or more high-voltage or low-voltagethresholds. Actions can include sending a message, such as an emailnotification, sending an SMS notification. According to embodiments,actions can also include triggering an alarm, for example, illuminatingan indictor and sounding an audible alarm device.

By way of example, actions corresponding to the violation of ahigh-voltage threshold can include, but are not limited to, reducing aclock frequency of a heat-producing electronic component within theelectronic system 102, reducing power supplied to the electronic system102, increasing cooling of the electronic system 102 and disconnectingpower from the electronic system 102. Similarly, in some embodiments,actions corresponding to the violation of a low-voltage threshold caninclude, but are not limited to sending a message, such as an emailnotification, sending an SMS notification or triggering an alarm, suchas a visual indictor or audible alarm.

In some embodiments, the action can include deleting encryption keyswithin a cryptography module, sending an email notification, sending anSMS notification or illuminating an indictor and sounding an audiblealarm. Some embodiments of the present disclosure can allow fordetection and reaction to attempted, unauthorized inspections of acryptographic module or device. Embodiments of the present disclosurecan provide an indication of an attempted physically intrusiveinspection of a secure or cryptographic circuit without imposingpermanent and/or negative effects on the functionality of the device orcircuit in which it is deployed.

It can be understood that response device 120 can be configured torespond to violations of multiple thresholds with different and uniqueaction to each threshold violation. A non-limiting listing of actiontypes has been provided and described above, however, other types arepossible. Once the action has been initiated, the method 400 returns tooperation 404.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for designing an electronic system fortemperature monitoring, the method comprising: receiving designrequirements for the electronic system; characterizing dielectric andadhesive materials that are candidates for use in the electronic system;choosing, from candidate dielectric and adhesive materials, dielectricand adhesive materials in accordance with the design requirements;designing a characterized dielectric to include chosen dielectric andadhesive materials; fabricating the characterized dielectric inaccordance with a characterized dielectric design; and integrating thecharacterized dielectric into the electronic system by: populating theelectronic system with a plurality of heat-producing electronic devices;and electrically interconnecting the characterized dielectric to aleakage measurement circuit.
 2. The method of claim 1, wherein thecharacterized dielectric includes a dielectric layer of a PCB, a firstface of the dielectric layer adjacent to a first conductive layer of thePCB, and an opposing face of the dielectric layer adjacent to a secondconductive layer of the PCB.
 3. The method of claim 1, wherein thecharacterized dielectric includes a dielectric layer of a flexiblecircuit, a first face of the dielectric layer adjacent to a firstconductive layer of the flexible circuit, and an opposing face of thedielectric layer adjacent to a second conductive layer of the flexiblecircuit.
 4. The method of claim 3, wherein integrating the characterizeddielectric into the electronic system includes locating the flexiblecircuit adjacent to the plurality of heat-producing electronic devices.5. The method of claim 1, wherein characterizing candidate dielectriclayer and adhesive materials includes characterizing electrical leakageproperties, including temperature-dependant electrical leakagevariation, of the candidate dielectric and adhesive materials.
 6. Themethod of claim 1, wherein the candidate dielectric and adhesivematerials include materials selected from the group consisting of: aFire Retardant (FR) laminate materials layer, a High Temperature (HT)laminate materials layer and an Adhesive-less/high-Performance (AP)laminate materials layer.
 7. The method of claim 1, wherein the choosingof a dielectric material in accordance with the design requirementsincludes selecting a dielectric material having a temperature-dependentelectrical leakage variation, over an operating temperature range, inaccordance with the design requirements.
 8. The method of claim 1,further comprising choosing, in accordance with the design requirements,a supplemental dielectric material, and wherein the designing of thecharacterized dielectric includes the dielectric material and thesupplemental dielectric material.
 9. A method for designing anelectronic system for temperature monitoring, the method comprising:receiving design requirements for the electronic system, the designrequirements including specified leakage characteristics for acharacterized dielectric; characterizing dielectric and adhesivematerials that are candidates for use in the electronic system;choosing, from candidate dielectric and adhesive materials, dielectricand adhesive materials in accordance with the specified leakagecharacteristics; and designing a characterized dielectric to includechosen dielectric and adhesive materials.
 10. The method of claim 9,further comprising: fabricating the characterized dielectric inaccordance with a characterized dielectric design; and electricallyinterconnecting the characterized dielectric to a leakage measurementcircuit.
 11. The method of claim 10, wherein the leakage measurementcircuit is configured to measure the current leakage through thecharacterized dielectric and convert current measurement into acorresponding output voltage.
 12. The method of claim 11, furthercomprising electrically connecting a response device to the leakagemeasurement circuit, the response device configured to initiate anaction in response to the output voltage exceeding a voltage threshold.13. The method of claim 9, wherein the characterized dielectric includesa dielectric layer of a PCB, a first face of the dielectric layeradjacent to a first conductive layer of the PCB, and an opposing face ofthe dielectric layer adjacent to a second conductive layer of the PCB.14. A method for designing an electronic system for temperaturemonitoring, the method comprising: providing specified leakagecharacteristics for a characterized dielectric; providing electricalleakage properties for candidate dielectric and adhesive materials; anddesigning a characterized dielectric based on the specified leakagecharacteristics and the candidate dielectric materials.
 15. The methodof claim 14, further comprising: fabricating the characterizeddielectric in accordance with a characterized dielectric design; andelectrically interconnecting the characterized dielectric to a leakagemeasurement circuit.
 16. The method of claim 15, wherein the leakagemeasurement circuit is configured to measure the current leakage throughthe characterized dielectric and convert current measurement into acorresponding output voltage.
 17. The method of claim 16, wherein theleakage measurement circuit is configured to measure the current leakagethrough the characterized dielectric and convert current measurementinto a corresponding output voltage.
 18. The method of claim 17, furthercomprising electrically connecting a response device to the leakagemeasurement circuit, the response device configured to initiate anaction in response to the output voltage exceeding a voltage threshold.19. The method of claim 14, wherein the characterized dielectricincludes a dielectric layer of a PCB, a first face of the dielectriclayer adjacent to a first conductive layer of the PCB, and an opposingface of the dielectric layer adjacent to a second conductive layer ofthe PCB.